Deer zappers and DSL outages
I used to live pretty far out in the boonies as far as technology went. I was just barely able to get DSL from the telco, but it would freak out and do all sorts of stupid things at times. They wouldn't provision it higher than 128 kbps up and 384 kbps down. Many times, I'd wake up and look at it to find that my DSL bridge had frozen overnight and took down the circuit.
The telco sent some techs out to replace the modem, but that really didn't help, either. It seemed to improve a little, but it was still considerably less than the reliability I had gotten from ISDN and even dialup in the years before it.
Then, one day, it went down and stayed down. The physical plant people at the telco said my cable and pair were "perfect" and that there was nothing wrong. It just wouldn't sync reliably at any speed, even the lowest they offered (384).
During this, I had to go out to run some errands. Upon returning, I was walking down my driveway and heard this weird buzzing noise coming from my neighbor's yard. It had the same duty cycle as this annoying buzz I had heard on my shortwave radio at times. It was on for the same amount of time, and then off for the same amount of time.
I walked over and looked. We called this guy the "lawn nazi" because he was super protective of his front yard. This extended to the point of asking us to not mow past the property line even if it was just two more feet to where his driveway was. This guy once shot an armadillo which crawled into our yard and died because it was digging holes in his back yard. Anyway, it turned out he had taken his lawn protection to the next level by installing a deer zapper.
Yep, all of the bushes in his front yard were wired up with some kind of conductive material, and it was plugged into a transformer of some sort. It looked like it was set to pulse, but there was a problem: it was shorting into the wet ground and was making an audible noise. It was enough of a spark gap transmitter to splat all over a wide swath of spectrum, and that was getting into my radio.
It started making sense. Given that phone lines aren't usually particularly well-shielded, that the DSL modem/bridge was in the room nearest his deer zapper, and DSL uses high-frequency encoding, why not? That and the seemingly random behavior made it a definite possibility.
Later on, it either shut down or dried out and stopped arcing, and the noise disappeared from my radio. My DSL also came back up by itself.
While it's not a certainty, it's the best explanation I ever had for it.
I imagine this still affects people with marginal connections. I would recommend getting a feel for the local RF situation when things start going crazy. You never know when one thing is going to leak into something else and make your life miserable.